1. Field of the Invention
This invention relates to grass cutting devices. The invention relates more particularly to an improved form of electrically energized device for trimming grass at difficult to reach locations.
2. Description of the Prior Art
Various electrically energized grass cutting devices are known for close trimming of grass and vegetation in areas which are difficult to reach. These areas comprise, for example, the areas immediately around the base of fence pickets and posts, around tree trunks, around bushes, along walls and about other structural objects and which are otherwide inaccessible to full sized lawn mowing devices. In the past, the design of such trimming devices has represented a compromise of contrasting requirements. On the one hand, trimming is enhanced by use of a cutting head which provides sufficient exposure of a rotating cutter blade so that the blade has access to the vegetation in close proximity to the structure. Grass about the object can then be cleanly cropped. On the other hand, exposure of the cutting blade increases the likelihood of blade impact with the structure and with other random objects, such as stones, thus increasing the possibility of breakage of the blade. Not only does blade breakage necessitate replacement and increase the cost and inconvenience of operation, but its impact with an object can result in a dangerous propelling of relatively small objects or of a fractured blade segment. In addition, since the blade is rotated at a relatively high rate, an exposed metal trimmer blade presents a potential hazard to the person of the user.
Accordingly, a metal blade grass trimmer has evolved which includes a housing having a protective skirt extending about the rotating metal blade. This skirt reduces contact between a rotating blade and the ground, structures and stones; it deflects projectiles resulting from blade impacts; and, it establishes a degree of personal protection to the user from a cuting edge of the blade. One such form of electrically energized trimming device provides for rotating a relatively sharp metal blade of small diameter, as, for example 3-1/2 inches. This blade which is rotated at a relatively high rate is supported in a housing and is circumscribed by a protective, toothed skirt or shroud. The skirt inhibits the rotating blade from touching the ground while the tooth perforations enable vegetation to extend through the skirt into the housing for shearing by the rotating blade. While the blade can be placed directly over the area to be trimmed, trimming with a sweeping motion of this device is limited since access between the grass to be cut and the blade is limited by the toothed blade skirt. In addition, a rapidly rotating blade of this device retains the capacity to cause projectiles and is subject to frequent breakage.
An alternative form of grass trimmer which has gained acceptance provides for rotation of a relatively small diameter line of a flexible material such as a polymer plastic formed from nylon. The line which extends from a hub is rotated at a speed sufficiently high to stiffen the line for shearing grass. This trimmer arrangement is advantageous principally because of the flexibility of the line material. A flexible line yields to objects and at times conforms to structures such as a wall base thereby reducing breakage and eliminating projectiles as well as providing enhanced trimming in places difficult to reach with a metal blade trimmer. In addition, while impact with a hand or foot of a person may bruise, the line substantially reduces serious injury. The line trimmer is however subject to greater wear than a metal blade and must frequently be replaced to maintain cutting efficiency. The inconvenience of replacing the cutting line is reduced to some extent by the provision of an automatic line feeder which, however, increases both the complexity and the cost of the apparatus and reduces its reliability.
We have found that grass trimmer devices can be used which employ flexible strip cutter blades of relatively low mass. We have discovered that the blades which are formed, for example, of a strip of a polymer material have exhibited a tendency to depart from an initial cutting plane upon impacting objects and to dwell temporarily at different cutting planes thus creating an undesirably uneven and scalloped appearing cut. Furthermore, these blades are subject to frequent breakage.
An important aspect of electrically energized grass trimming devices of the type described is portability. It is preferable that the trimming device be cordless and derive its electrical energy from a self contained battery power pack. It is found, however, that the line trimmer requires substantial energy while undulations between cutting planes of the strip trimmer is wasteful of energy. Both of these characteristics contribute undesirably to the size and weight of a battery pack required to attain extended usage.